Rapid and selective quantification of sulfite in complex aqueous matrices across a wide concentration range via...

Accurate and reliable sulfite detection is essential for ensuring food safety and environmental compliance. Herein, a sulfur dioxide-mediated microwave resonant sensing strategy is employed for sulfite quantification. The approach is based on the chemical conversion of sulfite ions (SO₃^2-) into sulfur dioxide (SO₂) gas via acidification, followed by the detection of dielectric changes in the sensing layer induced by gas-phase adsorption. An open split-ring resonator (SRR) based microwave sensor was designed and integrated with two different sensing materials: hydrogen peroxide (H₂O₂) and a SnO₂-polyaniline (SnO₂-PANI) composite, to investigate and compare their sensing properties. Electromagnetic field distribution, surface current density, and reflection coefficient (S₁₁) responses were simulated using ANSYS High Frequency Structure Simulator (HFSS). Experimental results reveal that the H₂O₂-based sensor exhibits an exceptional variation in S₁₁ amplitude with high sensitivity over a sulfite concentration range of 8-320 mg/L, achieving a limit of detection (LOD) of 2.93 mg/L. In contrast, the SnO₂-PANI-based sensor demonstrates a strong linear relationship between the frequency shift and sulfite concentration in the range of 8-480 mg/L, with a limit of detection (LOD) of 4.94 mg/L. Multivariate analysis incorporating frequency shift, bandwidth, S₁₁ response, and normalized quality (Q) factor confirms that both sensors effectively capture dielectric constant and loss changes caused by SO₂ adsorption. Furthermore, its practical applicability was demonstrated through the determination of target SO₃^2- levels in diverse water samples. Offering rapid response and operational simplicity, this microwave-assisted approach represents a reliable alternative to conventional sulfite detection methods with broad application potential.